Surgery frequently requires the grasping or cutting of tissues and organs situated at some distance from the surgeon's hand, such as within a body cavity. In particular, endoscopic surgery often requires that the surgical site be a substantial number of centimeters from the initial incision. In endoscopic surgery, relatively small incisions are made by means of a trocar. The work is observed by means of a slender optical device (endoscope) inserted through a small incision into which a cannula may be placed. Endoscopic techniques, which are minimally invasive and relatively non-traumatic, are displacing conventional open surgery for many procedures, and instruments for endoscopy are proliferating.
A typical instrument employed in endoscopic surgery has a pair of articulated jaws, and a handle mechanism comprising two members, one movable with respect to the other, which can conveniently be manipulated so as to cause the jaws to open and close. Serrations, blades, or other features (depending upon the use for which the tool is intended) enable the jaws to perform various surgical functions, such as grasping or cutting. The articulated jaws are located at the distal end of a relatively long extension of the handle mechanism. The length of the shaft extension is determined by the depth of the surgical site, while its cross-sectional dimensions are established by the maximum permissible incision size.
Many ingenious linkages have been devised for converting the surgeon's manual efforts at the handle end of the instrument into opening and closing of the tool's jaws. Typically, although with some exceptions, the handle has a stationary member rigidly joined to a hollow shaft and a movable member pivotally attached to an operating rod that is mounted and is capable of reciprocal movement within the shaft. When the surgeon squeezes the stationary and movable handle members together, the operating rod acts upon the jaws (to which it is rotatably fastened by pins, or by tracks or levers kinematically equivalent to pins) in such a way as to make the jaws close. When the surgeon spreads the stationary and movable members apart, the motions are reversed and the jaws open. The jaws are rotatably attached to the end of the shaft by known means, e.g., by pins or kinematically equivalent tracks. In some cases, levers or other intermediate pieces are interposed between the operating rod and the jaws for causing the latter to open and close in response to relative movement of the stationary and movable handle members.
Although their constructional details and relationships to each other vary widely, such pins, tracks, levers, and other connecting components tend to preclude the presence, or limit the size, of a bore in the instrument through which an ancillary device, e.g., a fiber optic light guide, may be introduced adjacent to or between the jaws. These components cannot be miniaturized without limit, for reasons of strength; nor can they be relocated without disturbing the critical geometry of the linkages. Furthermore, it is not advisable to increase the shaft's diameter, which would necessitate a larger incision and detract from the benefits of the endoscopic method.
When operating the jaws of typical tools as described above, surgeons have experienced difficulty in grasping slippery tissues because the jaws close first at their rear ends and thereby tend to propel or push the tissues out from between the jaws. Consequently trauma of the tissues may result from repeated and increasingly aggressive attempts to grasp the tissue.